A thermal processing chamber as used herein refers to a device that rapidly heats objects, such as semiconductor wafers. Such devices typically include a substrate holder for holding a semiconductor wafer and a thermal energy source, such as a light source that emits light energy for heating the wafer. During heat treatment, the semiconductor wafers are heated under controlled conditions according to a preset temperature regime. For monitoring the temperature of the semiconductor wafer during heat treatment, thermal processing chambers also typically include temperature sensing devices, such as pyrometers, that sense the radiation being emitted by the semiconductor wafer at a selected band of wavelengths. By sensing the thermal radiation being emitted by the wafer, the temperature of the wafer can be calculated with reasonable accuracy.
In alternative embodiments, instead of or in addition to using radiation sensing devices, thermal processing chambers can also contain thermocouples for monitoring the temperature of the wafers. Thermocouples measure the temperature of objects by direct contact.
Many semiconductor heating processes require a wafer to be heated to high temperatures so that various chemical and physical reactions can take place as the wafer is fabricated into a device. During rapid thermal processing, which is one type of processing, semiconductor wafers are typically heated by arrays of lights to temperatures, for instance, from about 400° C. to about 1,200° C., for times which are typically less than a few minutes. During these processes, one main goal is to heat the wafers as uniformly as possible.
More particularly, in the past, semiconductor wafers were heated according to a predetermined heating cycle. For instance, the wafers were typically heated from an initial temperature to a desired temperature at a very fast heating rate. The wafers were then maintained at the desired temperature for a time sufficient for desired processes to take place. For instance, during these heating cycles the wafers can be annealed or various coatings and films can be deposited onto the wafers, such as oxide films.
In order to complete the heating cycle, the light sources are switched off and the wafers were allowed to cool after being maintained at a desired temperature for a predetermined amount of time. In general, the wafers were allowed to cool naturally by simply removing or turning off the heating source. In particular, the wafers would cool by the loss of energy through radiation from a hot body. The amount of energy that is lost from the wafer is proportional to the difference between the temperature of the wafer and the temperature of the surrounding atmosphere. Consequently, during these processes, the cooling rate of the wafers is relatively fast at high temperatures and then slows down exponentially as the temperature of the wafer decreases.
Recently, emphasis has been placed upon forming integrated circuits having thinner and more uniform layers that are more efficient and require less power to operate. In this regard, recent focus has turned to not only more precisely forming coatings and films in thermal processing chambers but also on reducing the length of time it takes to complete a heating cycle in the chamber. Unfortunately, however, conventional methods for cooling wafers in thermal processing chamber have frustrated these objectives.
For instance, as described above, conventional methods for cooling wafers in thermal processing chambers have a tendency to greatly increase the time it takes to complete a heating cycle within the chamber in that the wafers are cooled relatively slowly. Further, during this slow cooling phase of the cycle, unwanted chemical and physical reactions can occur which can adversely affect the electrical properties of coatings and films formed on the semiconductor wafer.
As such, a need currently exists for an improved apparatus and process for cooling wafers in rapid thermal processing chambers. In particular, a need currently exists for a rapid thermal processing chamber that is capable of actively cooling semiconductor wafers very rapidly after the wafers have been heated.